1. Field of the Invention
This invention relates generally to systems and methods for the treatment of cancer using radiation and, more specifically, to systems and methods for the treatment of cancer using implanted brachytherapy seeds.
2. Background and Summary of the Invention
Brachytherapy, a useful technique for treating cancer, is a radiation treatment using a solid or enclosed radioisotopic source positioned on the surface of the body or a short distance from the area to be treated. With respect to the treatment of prostate cancer, for example, brachytherapy involves the implantation of radiotherapy seeds into the prostate. The effectiveness of the brachytherapy treatment depends, however, on the particularized placement of the implanted brachytherapy seeds to achieve a preferred radiotherapy dose.
The radiotherapy dose administered to the patient may be calculated by determining the three dimensional (3D) positions of the brachytherapy seeds with respect to the affected tissue. In practice, computed tomography (CT) imaging is typically used after the implant to determine both the boundaries of the affected tissue and the locations of the implanted seeds. However, most operating rooms do not have CT equipment. This makes it difficult or impossible to evaluate and subsequently adjust the dose of radiotherapy to the patient during the implant (i.e. intraoperatively). Post-operatively, if “cold spots” are found, the patient must be re-treated.
In order to intraoperatively evaluate the dosimetry to the patient imaging modalities commonly found in an operating room must be used. For many procedures, ultrasound is the preferred modality for visualizing the tissue boundaries, and fluoroscopy (X-ray) imaging is the preferred modality for visualizing the brachytherapy seeds. Despite the development of more echogenic seeds (e.g. Amersham EchoSeed™) and more sophisticated ultrasound imaging devices, it remains difficult for human observers to accurately identify implanted seeds in ultrasound data. Because seeds reflect more sound energy than tissue, they show up as relatively bright spots in the ultrasound image. Fluoroscopy images clearly show the projected 2D positions of the seeds. Because seeds absorb more X-ray energy than tissue, they show up as relatively dark spots in the fluoroscopy image. However, tissue boundaries are not clearly visualized in fluoroscopy images.
Related U.S. patent application Ser. No. 09/875,031, filed Jun. 7, 2001, discloses systems and methods for determining the positions of implanted seeds using, at least in part, markers placed inside a patient. The markers are point objects capable of being visualized in both ultrasound and fluoroscopy images. They provide the “tie points” needed to register the fluoroscopy coordinate system with the ultrasound coordinate system. In this approach, markers and tissue boundaries are visualized with ultrasound and markers and seed positions are visualized with fluoroscopy. By reconstructing 3D seed positions from the fluoroscopy images and registering them to the ultrasound images through the use of the markers, the seed positions may be localized with respect to the affected tissue boundaries and the radiotherapy dose to the patient calculated.
It is generally known that placing markers around an affected tissue provides a better geometry for registration. For example, it is known that registration is impossible if all markers lie on the same 3D line or within the same 3D plane. Various systems, such as gold seeds, needle tips, and a “dummy” probe, have been used to provide markers around affected tissue. However, as will be apparent from the following discussion, each of these systems has its disadvantages.
Gold seeds have been used as fiducial markers. Existing gold seeds, which are FDA-approved for permanent implantation, are well visualized in fluoroscopy images, but less well visualized in ultrasound images. In order to provide a geometry for better registration, the gold seeds are typically placed around an affected tissue. However, in certain situations, it may be difficult or impossible to place the gold seeds in this manner. Furthermore, gold seeds in the ultrasound images may not be easily located by either existing software or physicians. Errors in locating the gold seeds in the ultrasound images may subsequently cause an inaccurate determination of ultrasound seed positions.
Implant needle tips have been used as fiducial markers. In this technique, after inserting the seeds, the physician inserts several needles into the patient. The needle tips serve as fiducials and must be located in both the ultrasound and fluoroscopy images. Although most of the needle is well visualized in a fluoroscopy image, because the needle tip narrows to a point, the position of the tip is generally fuzzy and difficult to locate accurately. In addition, physicians may be reluctant to insert additional needles into the patient (e.g., through unused holes of a template that was previously used for inserting seeds). Furthermore, the needle tips in the ultrasound images may not be easily located by either software or physicians. Errors in locating the needle tips may subsequently cause an inaccurate determination of ultrasound seed positions.
Points on a “dummy” probe have been used as fiducial markers. In this technique, especially with regards to prostate brachytherapy applications, the physician inserts a “dummy” radio-translucent probe into the patient on which fiducial markers have been placed. The marker positions are determined by calibration, and therefore do not need to be identified in the ultrasound. The disadvantage of using this technique is that the fiducial markers are located in a nearly coplanar region and provide a very poor geometry for registration. Small errors in locating the markers in the fluoroscopy images may lead to rather large errors in the subsequently determined ultrasound seed positions.
Therefore, it would be advantageous to provide a system and/or a method that provides the capability of determining the 3D positions of brachytherapy seeds without requiring use of fiducial markers or CT imaging.
The present invention provides a system and method for determining the 3D positions of one or more implanted radiotherapy seeds with respect to an area of affected tissue, such as the prostate, so that a radiotherapy dose may be calculated. The system and method may be used to determine the 3D positions of implanted brachytherapy seeds. Alternatively, the system and method may also be used to determine 3D positions of implanted objects (or implants) other than brachytherapy seeds. The system and method use ultrasound and fluoroscopy imaging and do not require CT imaging. Furthermore, the system and method do not require the use of markers placed inside the patient.
In one aspect, the invention provides a system and a method for determining the dosimetry of an implant with increased accuracy by determining the 3D positions of one or more seeds in the most recently acquired ultrasound treatment volume, or group of ultrasound treatment data.
The present invention also provides a system and method for determining the 3D positions of one or more implanted radiotherapy seeds with respect to an area of affected tissue such that the dosimetry to the affected tissue may be determined intraoperatively, permitting dynamic adjustment of a treatment plan.
The present invention further provides a system and method for allowing visualization of a 3D geometry of an implant by providing an interactive, computer-generated, graphical user interface.
Other aspects and features of the invention will be evident from reading the following detailed description of the preferred embodiments, which are intended to illustrate, not limit, the invention.